Imaging techniques such as magnetic resonance imaging (MRI), positron emission tomography (PET), and computed tomography (CT scan) provide non-destructive diagnostic examination of tissues or organs. In particular, PET involves the acquisition of physiologic images based on the detection of positron radiation emitted from a radioactive substance administered to the patient. The subsequent images of the human body developed with this technique are used to evaluate a variety of diseases, particularly cancer. Targeted delivery of the radioactive substance to the tissue or organ has advantages such as excellent specificity and high binding affinity, and therefore, has received considerable attention from the industry. Accordingly, there is a desire for substances that target and deliver positron-emitting radionuclides to selected organs or tissues.